<s>
The	O
uIP	B-Protocol
is	O
an	O
open-source	B-Application
implementation	O
of	O
the	O
TCP/IP	B-Protocol
network	I-Protocol
protocol	O
stack	O
intended	O
for	O
use	O
with	O
tiny	O
8	O
-	O
and	O
16-bit	O
microcontrollers	B-Architecture
.	O
</s>
<s>
It	O
was	O
initially	O
developed	O
by	O
Adam	O
Dunkels	O
of	O
the	O
Networked	O
Embedded	B-Architecture
Systems	I-Architecture
group	O
at	O
the	O
Swedish	O
Institute	O
of	O
Computer	O
Science	O
,	O
licensed	O
under	O
a	O
BSD	O
style	O
license	O
,	O
and	O
further	O
developed	O
by	O
a	O
wide	O
group	O
of	O
developers	O
.	O
</s>
<s>
uIP	B-Protocol
can	O
be	O
very	O
useful	O
in	O
embedded	B-Architecture
systems	I-Architecture
because	O
it	O
requires	O
very	O
small	O
amounts	O
of	O
code	O
and	O
RAM	O
.	O
</s>
<s>
It	O
has	O
been	O
ported	O
to	O
several	O
platforms	O
,	O
including	O
DSP	B-General_Concept
platforms	O
.	O
</s>
<s>
In	O
October	O
2008	O
,	O
Cisco	O
,	O
Atmel	O
,	O
and	O
SICS	O
announced	O
a	O
fully	O
compliant	O
IPv6	B-Protocol
extension	O
to	O
uIP	B-Protocol
,	O
called	O
uIPv6	O
.	O
</s>
<s>
uIP	B-Protocol
makes	O
many	O
unusual	O
design	O
choices	O
in	O
order	O
to	O
reduce	O
the	O
resources	O
it	O
requires	O
.	O
</s>
<s>
uIP	B-Protocol
's	O
native	O
software	O
interface	O
is	O
designed	O
for	O
small	O
computer	O
systems	O
with	O
no	O
operating	O
system	O
.	O
</s>
<s>
The	O
hardware	O
driver	O
is	O
called	O
after	O
uIP	B-Protocol
is	O
called	O
.	O
</s>
<s>
uIP	B-Protocol
builds	O
the	O
packet	O
,	O
and	O
then	O
the	O
driver	O
sends	O
it	O
,	O
and	O
optionally	O
receives	O
a	O
response	O
.	O
</s>
<s>
It	O
is	O
normal	O
for	O
IP	B-Protocol
protocol	I-Protocol
stack	O
software	O
to	O
keep	O
many	O
copies	O
of	O
different	O
IP	B-Protocol
packets	O
,	O
for	O
transmission	O
,	O
reception	O
and	O
to	O
keep	O
copies	O
in	O
case	O
they	O
need	O
to	O
be	O
resent	O
.	O
</s>
<s>
uIP	B-Protocol
is	O
economical	O
in	O
its	O
use	O
of	O
memory	O
because	O
it	O
uses	O
only	O
one	O
packet	O
buffer	O
.	O
</s>
<s>
Also	O
,	O
when	O
uIP	B-Protocol
needs	O
to	O
retransmit	O
a	O
packet	O
,	O
it	O
calls	O
the	O
application	O
code	O
in	O
a	O
way	O
that	O
requests	O
for	O
the	O
previous	O
data	O
to	O
be	O
reproduced	O
.	O
</s>
<s>
Another	O
oddity	O
is	O
how	O
uIP	B-Protocol
manages	O
connections	O
.	O
</s>
<s>
Most	O
IP	B-Protocol
implementations	O
have	O
one	O
task	O
per	O
connection	O
,	O
and	O
the	O
task	O
communicates	O
with	O
a	O
task	O
in	O
a	O
distant	O
computer	O
on	O
the	O
other	O
end	O
of	O
the	O
connection	O
.	O
</s>
<s>
In	O
uIP	B-Protocol
,	O
no	O
multitasking	O
operating	O
system	O
is	O
assumed	O
.	O
</s>
<s>
On	O
each	O
call	O
,	O
uIP	B-Protocol
tries	O
to	O
serve	O
a	O
connection	O
,	O
making	O
a	O
subroutine	O
call	O
to	O
application	O
code	O
that	O
responds	O
to	O
,	O
or	O
sends	O
data	O
.	O
</s>
<s>
The	O
size	O
of	O
the	O
connection	O
array	O
is	O
a	O
number	O
that	O
can	O
be	O
adjusted	O
when	O
uIP	B-Protocol
is	O
recompiled	O
.	O
</s>
<s>
uIP	B-Protocol
is	O
fully	O
compliant	O
with	O
the	O
RFCs	O
that	O
define	O
TCP	B-Protocol
,	O
UDP	B-Protocol
and	O
IP	B-Protocol
.	O
</s>
<s>
It	O
also	O
implements	O
the	O
mandatory	O
maintenance	O
protocol	O
ICMP	B-Protocol
.	O
</s>
<s>
uIP	B-Protocol
0.9	O
is	O
the	O
version	O
with	O
the	O
least	O
dependence	O
on	O
operating	O
systems	O
,	O
the	O
smallest	O
resource	O
use	O
,	O
and	O
the	O
only	O
version	O
that	O
presents	O
a	O
pure	O
event	O
loop	O
API	B-General_Concept
,	O
but	O
in	O
its	O
original	O
form	O
does	O
not	O
support	O
IP	B-Protocol
version	I-Protocol
6	I-Protocol
,	O
only	O
the	O
older	O
,	O
more	O
common	O
IPv4	O
.	O
</s>
<s>
It	O
may	O
be	O
used	O
in	O
embedded	B-Architecture
systems	I-Architecture
with	O
very	O
small	O
amounts	O
of	O
resources	O
.	O
</s>
<s>
It	O
was	O
delivered	O
with	O
a	O
set	O
of	O
examples	O
of	O
higher-level	O
protocols	O
that	O
also	O
run	O
on	O
an	O
event	O
loop	O
system	O
,	O
including	O
HTTP	B-Protocol
(	O
a	O
simple	O
web	O
server	O
)	O
,	O
SMTP	B-Protocol
(	O
simple	O
mail	O
transmission	O
protocol	O
)	O
,	O
FTP	B-Protocol
(	O
file	B-Protocol
transfer	I-Protocol
protocol	I-Protocol
)	O
,	O
telnet	B-Protocol
(	O
terminal	O
emulation	O
)	O
,	O
and	O
others	O
.	O
</s>
<s>
Despite	O
the	O
examples	O
and	O
its	O
small	O
size	O
,	O
uIP	B-Protocol
0.9	O
can	O
be	O
difficult	O
to	O
apply	O
because	O
it	O
does	O
not	O
use	O
any	O
form	O
of	O
socket	O
API	B-General_Concept
.	O
</s>
<s>
uIP	B-Protocol
is	O
widely	O
used	O
code	O
with	O
well-known	O
weaknesses	O
.	O
</s>
<s>
Also	O
,	O
16-bit	O
software	O
timers	O
(	O
common	O
on	O
small	O
microcontrollers	B-Architecture
)	O
can	O
overflow	B-Error_Name
and	O
cause	O
defective	O
operation	O
.	O
</s>
<s>
This	O
can	O
be	O
fixed	O
with	O
a	O
timer	O
system	O
that	O
does	O
not	O
overflow	B-Error_Name
(	O
e.g.	O
</s>
<s>
In	O
slow	O
,	O
serial	B-Protocol
port	I-Protocol
implementations	O
,	O
the	O
ack-throughput	O
can	O
be	O
fixed	O
by	O
modifying	O
uIP	B-Protocol
to	O
send	O
every	O
packet	O
as	O
two	O
half-packet	O
fragments	O
.	O
</s>
<s>
uIP	B-Protocol
systems	O
with	O
fast	O
ethernet	O
or	O
WiFi	O
can	O
modify	O
the	O
hardware	O
driver	O
to	O
send	O
every	O
packet	O
twice	O
.	O
</s>
<s>
Some	O
PCs	O
do	O
not	O
correctly	O
respond	O
to	O
a	O
fast	O
uIP	B-Protocol
system	O
on	O
a	O
local	O
ethernet	O
,	O
because	O
the	O
uIP	B-Protocol
system	O
can	O
start	O
a	O
responding	O
packet	O
before	O
the	O
PC	O
is	O
ready	O
to	O
receive	O
it	O
.	O
</s>
<s>
The	O
solution	O
is	O
to	O
call	O
the	O
uIP	B-Protocol
system	O
less	O
frequently	O
in	O
the	O
main	O
loop	O
(	O
Windows	O
PCs	O
are	O
designed	O
for	O
a	O
response	O
time	O
of	O
about	O
1	O
millisecond	O
)	O
.	O
</s>
<s>
Typical	O
implementations	O
of	O
uIP	B-Protocol
have	O
a	O
fixed	O
IP	B-Protocol
address	O
,	O
which	O
can	O
make	O
them	O
impractical	O
in	O
real	O
networks	O
,	O
although	O
some	O
have	O
implemented	O
DHCP	B-Protocol
.	O
</s>
<s>
Later	O
versions	O
of	O
uIP	B-Protocol
,	O
including	O
the	O
reference	O
version	O
of	O
uIPv6	O
,	O
are	O
integrated	O
with	O
Contiki	B-Operating_System
,	O
an	O
operating	O
system	O
that	O
uses	O
coroutines	B-Architecture
for	O
cooperative	O
multitasking	O
.	O
</s>
<s>
Contiki	B-Operating_System
provides	O
the	O
multitasking	O
needed	O
by	O
a	O
simplified	O
socket	O
API	B-General_Concept
,	O
simplifying	O
the	O
use	O
of	O
uIP	B-Protocol
.	O
</s>
